Coating for metal molds



i, l atented Feh. l6, i

costume; roe. METAL moths area stares 7' B AND FERICK.MILLER, 0F DETROIT, MICH' IGAN, GNORS T0 HOLLEY, OF DETROIT, "Pi

GAE"

no Drawing. Application filed December is, 192 Search. 154,646. Renewed June at, rear.

The object of this invention is to provide an improved protective .coating for metal molds in which metal castings are made. The specific object of this coating is to eliminate the necessity for smoking the molds, which has been found most essential with the coatings now in use when casting gray iron in the molds, if chilled. .avoided.

We have discovered that a mixture of G grade sodium silicate, Castor oil, lampblaclr and salicylic acid with water will =form a paste which, when applied to a heated metal (white) spots are to be mold, produce" a relatively thick coating] which is adherent, refractory, and a heat insulator which is not easily eroded by the ac tion of molten metal. I c

The proportions We have found suitable for protecting cast iron molds h-om the action of molten cast iron are as follows A. mixture ofw v i 20 parts, byweight, oi sodium silicate, A C grade. parts of castor oil) to parts of lampblack mixed with 5 parts Q3 oiwater. t 5 partsoi salicylic acid.

, (The salicylic acid is added'last for best results.) Tfixture B is added to mixture A. a

It must be understood that the sodium silicate is mixed in the liquid form as purchased,

containing of course a considerable quantity of W8.l781. The ingredients are mixed as follows The castor oil is first mixed with the diluw a solution of 0 grade sodium silicate. A-mil'd chemical action takes place, resulting in an 0 emulsion 0t saponified oil and silica 'gel. The castor oil is added until there is an excess,

causing the complete decomposition of the so- 1 dium silicate. Finally a mixture of five parts of salicylic acidand five parts of lampblack are added the want oil-sodium silicate emulsion, and the whole mixture is heated to the bolling point of water and vigorously stirred to ensure a uniform mixture. .Th'epaste or thick emulsion thus is applied as follows i The mold is heated to-at least 400 F. and the coating applied :with a brush. As salicylic acid meltsat slightly above 300 F, the effect of the heat of the mold on the coating is to make it much more fluid and therefore the application of the coating is facilitated,

as the coating becomes thinner and spreads eas1ly, covcr1ng a larger area with a tenacious coat ng.

Themold is then heated so as to causethe decomposition of the organic compounds. If a thicker coating is desired the mold is allowed to cool ,to 500 F. and then wrecoated and reheated. In practice from three to seven coatings will give the desired thickness, such a coating being .005" to .010" thick. I

In actual operation thecoating is repaired every 10 or 20 castings. If this is done it is found the mold will stand up indefinitely and the coating will not peel oil, which is the characteristic defect of existing coatings wherr an attempt is made to duplicatesuch q a thickness.

As castor oil acts as a saponifiable oil, another saponifiable oil might beused instead of castor oil with similar results. ple linseed oil or lard oil.

As far as the salicylic acid is concerned, tartaric,'benzoic, ta nnic acid 'or any other organic comp0und,'preferably an acid, may

.be used, the important thing being that the substitute should melt at about 300 E, which prepared fit) For examfacilitates the application of the coating as described above. v a

The ultimate structure is a very intimate mixture of very finely divided carbon and dehydrated silica el. Upon burning out the gel has much the appearance of a honey comb when eained under the microscope.

carbon we find t at thisv dehydrated silica L What we'claim isz-i 1. A coating paste for metal molds, comprising an emulsion with a dilute solution of sodium silicate in water and castor oil 5 mixed together With a small I quantity of salicylic acid and lamplolack mixed therein. 2. A coating for protecting iron molds, consisting of colloidal silica intimately mixed with very finely divided carbon deposited 1 from a suspension in water, the silica loeing deposited from a mixture of sodium silicate solution and a saponifiable" oil.

In testimony whereof We afix our signatures. v

HARRY 1P. KIMBER.

FREDERICK MILLER 

